/*

 * Copyright (c) 2020 Red Hat, Inc.

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version 2

 * of the License, or (at your option) any later version.

 * 

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 * 

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

 * 02110-1301, USA. 

 *

 * $Id: //eng/vdo-releases/aluminum/src/c++/vdo/base/waitQueue.c#1 $

 */

#include "waitQueue.h"

#include "permassert.h"

#include "statusCodes.h"

/**********************************************************************/

int enqueueWaiter(WaitQueue *queue, Waiter *waiter)

{

  int result = ASSERT((waiter->nextWaiter == NULL),

                      "new waiter must not already be in a waiter queue");

  if (result != VDO_SUCCESS) {

    return result;

  }

  if (queue->lastWaiter == NULL) {

    // The queue is empty, so form the initial circular list by self-linking

    // the initial waiter.

    waiter->nextWaiter = waiter;

  } else {

    // Splice the new waiter in at the end of the queue.

    waiter->nextWaiter = queue->lastWaiter->nextWaiter;

    queue->lastWaiter->nextWaiter = waiter;

  }

  // In both cases, the waiter we added to the ring becomes the last waiter.

  queue->lastWaiter   = waiter;

  queue->queueLength += 1;

  return VDO_SUCCESS;

}

/**********************************************************************/

void transferAllWaiters(WaitQueue *fromQueue, WaitQueue *toQueue)

{

  // If the source queue is empty, there's nothing to do.

  if (!hasWaiters(fromQueue)) {

    return;

  }

  if (hasWaiters(toQueue)) {

    // Both queues are non-empty. Splice the two circular lists together by

    // swapping the next (head) pointers in the list tails.

    Waiter *fromHead = fromQueue->lastWaiter->nextWaiter;

    Waiter *toHead   = toQueue->lastWaiter->nextWaiter;

    toQueue->lastWaiter->nextWaiter   = fromHead;

    fromQueue->lastWaiter->nextWaiter = toHead;

  }

  toQueue->lastWaiter   = fromQueue->lastWaiter;

  toQueue->queueLength += fromQueue->queueLength;

  initializeWaitQueue(fromQueue);

}

/**********************************************************************/

void notifyAllWaiters(WaitQueue      *queue,

                      WaiterCallback *callback,

                      void           *context)

{

  // Copy and empty the queue first, avoiding the possibility of an infinite

  // loop if entries are returned to the queue by the callback function.

  WaitQueue waiters;

  initializeWaitQueue(&waiters);

  transferAllWaiters(queue, &waiters);

  // Drain the copied queue, invoking the callback on every entry.

  while (notifyNextWaiter(&waiters, callback, context)) {

    // All the work is done by the loop condition.

  }

}

/**********************************************************************/

Waiter *getFirstWaiter(const WaitQueue *queue)

{

  Waiter *lastWaiter = queue->lastWaiter;

  if (lastWaiter == NULL) {

    // There are no waiters, so we're done.

    return NULL;

  }

  // The queue is circular, so the last entry links to the head of the queue.

  return lastWaiter->nextWaiter;

}

/**********************************************************************/

int dequeueMatchingWaiters(WaitQueue   *queue,

                           WaiterMatch *matchMethod,

                           void        *matchContext,

                           WaitQueue   *matchedQueue)

{

  WaitQueue matchedWaiters;

  initializeWaitQueue(&matchedWaiters);

  WaitQueue iterationQueue;

  initializeWaitQueue(&iterationQueue);

  transferAllWaiters(queue, &iterationQueue);

  while (hasWaiters(&iterationQueue)) {

    Waiter *waiter = dequeueNextWaiter(&iterationQueue);

    int     result = VDO_SUCCESS;

    if (!matchMethod(waiter, matchContext)) {

      result = enqueueWaiter(queue, waiter);

    } else {

      result = enqueueWaiter(&matchedWaiters, waiter);

    }

    if (result != VDO_SUCCESS) {

      transferAllWaiters(&matchedWaiters, queue);

      transferAllWaiters(&iterationQueue, queue);

      return result;

    }

  }

  transferAllWaiters(&matchedWaiters, matchedQueue);

  return VDO_SUCCESS;

}

/**********************************************************************/

Waiter *dequeueNextWaiter(WaitQueue *queue)

{

  Waiter *firstWaiter = getFirstWaiter(queue);

  if (firstWaiter == NULL) {

    return NULL;

  }

  Waiter *lastWaiter = queue->lastWaiter;

  if (firstWaiter == lastWaiter) {

    // The queue has a single entry, so just empty it out by nulling the tail.

    queue->lastWaiter = NULL;

  } else {

    // The queue has more than one entry, so splice the first waiter out of

    // the circular queue.

    lastWaiter->nextWaiter = firstWaiter->nextWaiter;

  }

  // The waiter is no longer in a wait queue.

  firstWaiter->nextWaiter  = NULL;

  queue->queueLength      -= 1;

  return firstWaiter;

}

/**********************************************************************/

bool notifyNextWaiter(WaitQueue      *queue,

                      WaiterCallback *callback,

                      void           *context)

{

  Waiter *waiter = dequeueNextWaiter(queue);

  if (waiter == NULL) {

    return false;

  }

  if (callback == NULL) {

    callback = waiter->callback;

  }

  (*callback)(waiter, context);

  return true;

}

/**********************************************************************/

const Waiter *getNextWaiter(const WaitQueue *queue, const Waiter *waiter)

{

  Waiter *firstWaiter = getFirstWaiter(queue);

  if (waiter == NULL) {

    return firstWaiter;

  }

  return ((waiter->nextWaiter != firstWaiter) ? waiter->nextWaiter : NULL);

}